US president Barack Obama has called the global climate talks an "act of defiance" against terrorism that proves the world stands undeterred by Islamic State-linked attacks in Europe and beyond.

Mr Obama used his speech to more than 150 world leaders to salute Paris and its people for "insisting this crucial conference go on" just two weeks after attacks that killed 130 in the French capital.

He said leaders had converged to show resolve to fight terrorism and uphold their values at the same time.

"What greater rejection of those who would tear down our world than marshalling our best efforts to save it," Mr Obama said.

His remarks came at the start of two weeks of make-or-break negotiations to finalise a sweeping global agreement to cut carbon emissions and hopefully stave off the worst effects of climate change.

Mr Obama exhorted leaders here to fight the enemy of cynicism - "the notion we can't do anything" about the warming of the planet.

After sketching dire threats of submerged nations, abandoned cities and ever-worsening flooding and natural disasters, Mr Obama insisted that grim future "is one that we have the power to change." He urged leaders to "rise to this moment," invoking the late Martin Luther King Jr's observation that there is such a thing as being too late to a cause.

"That hour is almost upon us," he said.

Efforts to secure a climate deal have been hampered by a long-running dispute about whether developing nations share the same burden as industrialised nations that have historically polluted much more. The US and other nations have insisted that all countries chip in under the new agreement.

"No nation - either wealthy or poor - is immune to what this means," Mr Obama said as he described spiralling effects of climate change if left unchecked.

Mr Obama met with President Xi Jinping of China, which has started taking aggressive action to curb emissions, and planned a similar meeting later in the day with India's prime minister Narendra Modi.

Mr Obama also met privately with Russian president Vladimir Putin. The US had been cautiously optimistic about closer cooperation with Russia in fighting the Islamic State group, but those hopes were dampened after US treaty ally Turkey shot down a Russian plane it said entered its airspace from Syria.

In his sit-down with Mr Xi, Mr Obama touted close cooperation on climate change as vital to world efforts on global warming, and said nowhere had coordination with Beijing been more critical or fruitful than on climate change. He credited US and Chinese leadership with leading 180 nations to make their own pledges to curb emissions in the run-up to the Paris talks.

"Our leadership on this issue has been absolutely vital," Mr Obama said. China emits about 30% of the world's greenhouse gases and the US about 16%.

Mr Xi, speaking through a translator, said that global worries made it even more important for the US and China to work together.

"The world economy is recovering slowly, terrorism is on the rise, and climate change is a huge challenge. There is more instability and uncertainty in international situations," said the Chinese leader.

As the conference kicked off, the Obama administration announced it was pledging 51 million US dollars (£34 million) to a global fund to help poorer countries adapt to climate change. The US contribution joins pledges from Germany, Canada, Italy and others to total 248 million US dollars (£165 million).

Israel's prime minister and the Palestinian president, in France for the climate summit, met and shook hands for the first time in years.

A photograph shows Benjamin Netanyahu and Mahmoud Abbas shaking hands and smiling on the sidelines of global climate talks outside Paris on Monday. It was not immediately clear if they had agreed to meet or if they spoke.

US mediated peace talks between the sides collapsed early 2014 and the two leaders have not met in years.

Meanwhile, leaders of small island nations pleaded for their survival, asking bigger countries to do more to cut emissions and help threatened nations cope with rising seas and wilder storms blamed on man-made global warming.

Peter M Christian, president of the Pacific nation of Micronesia, called on UN secretary-general Ban Ki-moon to declare a worldwide state of emergency.

Mr Christian said: "The challenge is to save ourselves, not someone else, but ourselves."

The prime minister of the Pacific country of Tuvalu, Enele Sosene Sopoaga, added that "any further temperature increase will spell the total demise of Tuvalu."

They spoke in Paris on the opening day of high-stakes climate talks aimed at reaching a global compromise to cut emissions long-term.

Bill Gates said he and other investors are pledging seven billion US dollars (£4.6 billion) for research and development of clean energy, and that they are hoping to get others to pitch in more in the coming days.

The Microsoft co-founder is announcing the investment as part of a larger initiative with world governments that are promising to double spending on renewable energy research.

Mr Gates told reporters that he is hoping to see more investors sign on "possibly this week." The money is being raised by individual wealthy investors and the University of California.

He said he has warned potential investors that new energy technologies take longer than IT or biotech to launch.

The fund will support a wide range of technologies, Mr Gates said - "biofuels, carbon capture, high wind, fission, fusion - we're unbiased but it has to be clean and possible to scale up cheaply".

And Mr Putin said Russia is ready to cut its greenhouse gas emissions by almost one-third over the next 15 years compared with 1990 levels - although the fall in Russia's economy since 1990 means that it could still increase its current emissions.

He said that by 2030 Russia is ready to bring its greenhouse gas emissions to 70% of their level in 1990.

Mr Putin also said that a future global climate deal must include commitments from both developing and developed countries.